The Florida senator, the presumptive front-runner for the 2016 Republican presidential nomination, could have taken the lead on any number of national issues. He chose the one that posed the greatest risk for a conservative: comprehensive immigration reform.

The issue has been a personal and political struggle for this son of Cuban immigrants. When he ran as a Tea Party candidate and won his Senate seat in 2010, he opposed a pathway to citizenship. But he reversed course when he joined the Gang of Eight and became the public face of the immigration bill that won Senate approval in late June and now faces long odds in the House.

"I don't think you want to live in a country where you have millions and millions of people that are here permanently but can never become U.S. citizens," Rubio told the Washington Examiner. "Why would we want to prevent someone who loves America from becoming an American?"

Immigration reform took on renewed political urgency after Mitt Romney won only 27 percent of the Hispanic vote in 2012, down from George W. Bush's 44 percent in 2004. Many leading Republicans argued that the GOP had to broaden its appeal to Hispanics and other minorities, but the party remains badly split. Of the 68 votes in favor of the Senate bill, only 14 were cast by Republicans.

If Rubio runs for president in three years, immigration reform could be the decisive issue in the Republican primaries, with Rubio having to fend off attacks from most of his rivals and a majority of Tea Party voters.

Rubio knew that taking on immigration reform was a gamble, but he really had no choice: The issue was going to come to him anyway. The news media or a debate moderator would surely ask why a prominent Hispanic leader would duck an issue of paramount importance to Hispanics.

If nothing else, his role in the Gang of Eight allowed him to cast immigration reform in a favorable political light. Rubio showed that he could work the levers of government, signaling GOP donors and key party operatives that he could do more than give a good speech: He could get things done.

"He chose to really lead, and when you lead you're going to take all the arrows — and you're going to take the arrows from all sides," said Rep. Mario Diaz-Balart, R-Fla. "The easy thing would have been for Marco Rubio to just talk about it and criticize and do nothing — and by the way, he would have been universally applauded."

"This is an issue that is politically a lose-lose," added Diaz-Balart, who is trying to negotiate a similar deal in the House.

Rubio's dogged pursuit of immigration reform is reminiscent of the determination he showed in 2009 when he thumbed his nose at the GOP establishment and launched a quixotic, underfunded Senate bid against a popular, moderate sitting governor of his own party. He ran as an unabashed conservative in the days immediately following President Obama's first inauguration, when some pundits questioned whether conservatism was dead.

The debate over the Senate immigration bill continues apace now that it moves to the House. But what is not debatable is the seasoned manner in which Rubio, a 42-year-old senator only midway through his first term, navigated the legislative tripwires even as social media and talk radio fired up the opposition.

"When you're in a rental car going from stop to stop, you better know why you're running, and you better be passionate about it," Rubio said recently when asked by a gathering of newspaper editors if he's eyeing the White House. Rubio is up for re-election in 2016 and has told reporters he would decide next year whether to seek another term in the Senate, run for president or pursue other opportunities.

Weighing heavily on the senator's decision is the time he spends in Washington every week, away from his wife and four young children, who live back home in Miami. Individuals familiar with Rubio's thinking believe that this factor — combined with the fact that he simply hasn't fallen in love with the Senate — could figure as prominently as political ambition when the Floridian decides whether to commit to another six-year term or seek higher office.

Rubio's decision to join the Gang of Eight was made with a potential presidential timeline in mind. The effort has alienated some Tea Party activists who propelled him to victory in 2010, as well as some mainstream Republicans. For a significant portion of grass-roots conservative activists, immigration is not just one issue among many, it is the issue.

While Rubio's ability to repair his relationship with this group could prove difficult, conservative activist Jon Fleischman, who publishes the FlashReport.org from his perch in Orange County, Calif., said the Tea Party is a diverse group with varied concerns, and not all Tea Partiers are going to dismiss Rubio, or necessarily be upset with him, because of immigration.

"Immigration is a sticky issue because with it comes a degree of intensity that you don't see on every issue," Fleischman said.

Despite it all, Rubio's cadre of supporters and informal advisers are upbeat.

Unlike Congress' 2007 attempt at immigration reform, this year's debate hasn't caused a full-scale revolt on the Right. Many credit Rubio's salesmanship for that, and his backers believe his willingness to invest the political capital he had earned from conservatives could pay off big, both in a Republican presidential primary and a general election campaign.

To that end, Rubio has assembled an experienced political team that is laying the foundation for a 2016 White House bid, should he decide to make the race. The senator's fundraising operation is modeled on the multicommittee architecture typical of presidential campaigns and designed to ease the process of contributing. His steering committee of about a dozen insiders includes well-connected Republicans like lobbyists Wayne Berman and Bill Paxon.

Major Republican power players believe Rubio's efforts on behalf of immigration reform would help him win over Hispanic voters — the nation's fastest-growing voting bloc — and broaden the party's appeal generally. At the very least, they predict, the political blowback from conservatives will have dissipated by the time the 2016 GOP primaries get under way.

Because of Rubio's positions on illegal immigration in his Senate campaign, his current support for a path to citizenship has opened him up to the sensitive charge of flip-flopping. But with his unalterably conservative voting record on almost every other issue in Congress, Rubio's supporters believe that his role in the Gang of Eight will be an overall positive, showing less partisan voters and the news media that he is willing to compromise with opponents to solve difficult problems.

One Republican political operative said Rubio shouldn't worry too much about people who say they won't vote for him because of immigration reform. "Chances are, in a crowded Republican primary, they probably weren't going to be with him in the first place," he said.